Reference for Eruvin 191:10
וסבר רבי עקיבא שבת זמן תפילין הוא והתניא ר"ע אומר יכול יניח אדם תפילין בשבתות וימים טובים ת"ל (שמות יג, ט) והיה לך לאות על ידך מי שצריכין אות יצאו אלו שהן גופן אות
- It<span class="x" onmousemove="('comment',' The ruling that the Passover sacrifice is only a positive commandment and the transgression of it does not, therefore, involve any of the penalties associated with a negative precept.');"><sup>30</sup></span> may be said to be in agreement even with the view of R'Akiba, for the expression 'Take heed' has the force of a negative precept only where it introduces a prohibitions but where it introduces a positive commandment<span class="x" onmousemove="('comment',' As in Ex. XIII, 10.');"><sup>31</sup></span> it has the force o a positive commandment.<span class="x" onmousemove="('comment',' Hence the ruling in the Mishnah of Ker. 2a. Lit., 'take heed of a " not"="" is="" not;="" take="" heed="" of="" a="" "do"="" do'.');"=""><sup>32</sup></span> But how could R'Akiba hold that the Sabbath is a time for wearing tefillin seeing that it was taught: R'Akiba stated: As it might have been presented that a man shall wear<span class="x" onmousemove="('comment',' Lit., 'lay', sc. on the arm and head.');"><sup>33</sup></span>